Updated

France's highest court upheld George Soros' conviction for insider trading Wednesday in a case dating back nearly 20 years, and the billionaire investor vowed to fight the ruling at the European Court of Human Rights.

The Court of Cassation upheld the 75-year-old American financier's conviction for buying and selling Societe Generale shares in 1988 after receiving information about a planned corporate raid on the bank. Apart from this case, Soros' record is unblemished after five decades in finance.

Lawyer Ron Soffer said Soros planned to take the case to the European Court of Human Rights, saying that the length of the proceedings prevented his client from having a fair trial.

"The investigation started in 1989," he said. "The appeals trial occurred in 2004. How can you call witnesses and ask them about what happened in 1988?"

Soffer also pointed out that France's stock market regulatory authority investigated the matter separately and concluded that Soros did not violate the law or any ethical rules.

French authorities have not yet determined what fine Soros will pay.

In a March 2005 ruling, a French appeals court confirmed a fine of euro2.2 million set by a lower court for the illegal purchase of 95,000 shares in Societe Generale. The Court of Cassation ruled that the fine would be adjusted to reflect Soros' profits, and it ordered the case returned to the appeals court to clarify the amount.

The Hungarian-born businessman has acknowledged that he was told about a Paris financier's plans to take over Societe Generale in late 1988 and began independently acquiring shares in the bank just days later.

But he denied that knowledge of the raid had amounted to insider information or influenced his transactions — which he said were part of a broader, documented strategy of investing in newly privatized French companies. Soros' lawyer said he cooperated with the case from the beginning.

Soros' spokesman, Michael Vachon, called the decision "an absurd miscarriage of justice" and said Soros was confident he would be cleared by the European court.

"As he has from the beginning, George Soros maintains that he engaged in no illegal or unethical conduct," Vachon said in a statement.

Soros, who emigrated to the United States in 1956 and set up Soros Fund Management 17 years later, has billions of dollars under management in his Quantum Fund.

He remains the only person convicted in the Societe Generale affair. Two others, Samir Traboulsi and Jean-Charles Naouri, were acquitted.

At an appeals hearing in 2005, Soros told the court his insider trading conviction had been a "gift to my enemies" in the United States and elsewhere. "My reputation is at stake," he said.

Soros has often drawn criticism for speculating heavily on the collapse of fragile currencies. In 2004 he also angered many conservatives in the United States by pumping US$27 million into election campaigns to try to unseat President George W. Bush.